1. Field of the Invention
The present invention relates to a bearing for a transmission for use on a drive shaft of a gearing device of a kind employed in, for example, an automobile transmission and, more particularly, to a technique that makes it possible to avoid an undesirable ingress of foreign matter into the bearing assembly, to reduce the seal torque and to reduce the shear resistance of an oil between a retainer and balls.
2. Description of Related Art
The ball retainer generally employed in the conventional ball bearings has a plurality of ball bearing pockets each being of a shape having a single curvature following the shape of each ball. Also, in order to enhance a lubricating condition, a ball retainer of a shape, in which each ball bearing pocket is depressed, is applied for patent. (See the patent documents 1 and 2 listed below.)
To avoid an undesirable ingress of foreign matter into the bearing assembly for a transmission, a contact type seal capable of sealing a bearing space is available. In such case, although a possible ingress of foreign matter can be avoided satisfactorily, a problem remains unsolved as to how the mechanical loss is reduced in order to pursue an increased mileage of an automotive vehicle. According to the related art, a technique of reducing the contact resistance at a sealing lip portion has been suggested to achieve a reduction of the mechanical loss. For example, shot peening is applied a contact type sealing lip slide surface to render the maximum roughness of the slide surface to be not greater than 2.5 μm so that the sealing torque can be reduced. (See the patent document 3 listed below.)